Trewhella, The Final Chapter?
We have the following from our correspondent Down Under, Rob Isdale:
World Wide Web has certainly lived up to its title.
One of the many visitors to Roy and Richard's Small Engine web site
recently, was Dennis Trewhella, and it was a pleasant surprise for him to see
and read the little article that I wrote about the Trewhella hot air engine that
Olaf Berge has built from the drawings and information in the 1897 patent number
Dennis lived in Victoria until his engineering occupation took him to England. After reading about William Trewhella, his grandfather’s younger brother, he found a telephone number for me in Brisbane, and through a few phone calls and emails to me and to Olaf, we have been interested to learn some further information about William Trewhella, his brother and the engineering business.
Dennis is able to add some important facts about William Trewhella's hot-air engine activities, and we have asked him to set out some of the details here, as an addition to my article. So, thank you Dennis, - it's over to you
was an engineer who set his mind to improving methods in the mill - the original
Trewhella jack being one of the first fruits of his efforts.
It proved a very useful implement for sawmillers, farmers and others,
having heavy lifting to do.
timber on the mill site was cut out by about 1893, when the brothers dissolved
partnership. William came to
Trentham and built the ‘Sunnyside Foundry’ to carry on jack
manufacture, while Benjamin continued as a sawmiller on various sites until
1903, when they joined in partnership again.
Benjamin took over a lot of the office work to give William more time for
developing new ideas. [KG 29 Sep 1964]
Trewhella's Patent Hot Air Motor
"There was a large attendance, including a number of ladies, to witness the public trial of the above motor, which took place at Mr. W. Trewhella's Sunnyside Iron Works on Saturday afternoon.
"Great Interest was taken in the working of
the motor, and the test was considered highly satisfactory.
leading features of the invention are perfect safety, great saving in fuel, and
entire saving of water.
The usual loss of time in getting up steam in
other engines is also saved and it is estimated that all the fuel used during
the trial, of some three or four hours, would not be sufficient to get up steam
in an ordinary steam engine of the same power.
"The present motor has been tested up to six h.p., and the amount of fuel consumed is from 3 lb. to 4 lb. per hour.
"In larger motors, the amount of fuel
required is expected to be less, and from the successful results of the present
one, there does not appear to be any limit to the amount of power that may be
obtained on the same principle.
"The power of the engine is obtained from
the expansion of air by heat; the exact and detailed operation of the mechanism
for effecting this purpose is not easily conveyed to the lay mind without the
aid of diagrams, but the principle is simple in action and easily understood.
"The lower or displacer piston is simply a
long, hollow vessel fitting the cylinder loosely, operated by means of a piston
rod passing through the power piston and connected with the outer mechanism, and
by its motion, draws in a charge of cool air under the power pistons at one
portion of the revolution, and later passes the charge through pipes into the
There it becomes heated by the combustion of the
fuel, and following well known laws of gases it expands, and in doing so, forces the piston out in the same manner as
steam in an ordinary steam engine.
"After having done its work, the air is
allowed to exhaust through a suitable valve and up the chimney.
"Fuel is fed into the furnace by means of a
drum revolving air-tight into a semi-cylindrical piston and having a number of
pockets in its circumference, each of which picks up a few coals from the
hopper, and in revolving drops them in. a passage in the piston into the
"In order to start the engine, a fire is
lit in the furnace and allowed to warm up a little, when the lighting door is
closed, and a pull at the fly-wheel starts the engine, the whole operation
taking but a few minutes.
"On larger engines, a reservoir of
compressed air may be used for starting.
"Much time and experiment has been devoted
to perfecting the details of the mechanism; also in controlling the heat, for
the hot air, like fire, is a bad master which has exhausted the resources of
many a scientist and engineer since the beginning of the century and a servant
which will, undoubtedly, encroach very largely on the realm of steam before the
"Arrangements have been made to exhibit the
motor at the exhibition at Ballarat, and it is to be sent there this week."
[KG 21 Jan 1896]
“Mr. Trewhella also
said that he remembers well the occasion and also that the engine was not
“At least four or
five were manufactured, but kerosene oil engines quickly superseded the hot air
“Mr. Trewhella said that the hot air engine,
of that time, was a rather heavy and cumbersome thing, weighing anything from
three to four tons for a six horsepower unit.
“Four or five of
these were manufactured at Trentham, but his uncle had lost heavily on those
manufactured as it had not proved to be a profitable undertaking.
“Yet he had had the satisfaction of putting
Trentham on the map at that time, as his machines created a lot of public
“The oil engine was being developed at the
same time and these could be constructed in a much smaller space and were much
“The boiler of the hot air and steam engines
was the main stumbling block.
“Mr. Trewhella said that his uncle had
designed his engine so that his fire was inside the cylinder. This was done to overcome the heat loss which was
a big factor against hot air engines. [KG 2 July 1966]
Maurice reminded me that there had been two large auctions of equipment at Trentham and nothing now remains. However, some years ago George Trewhella had commented that, in 1903, a disused air engine had been converted into a hydraulic pump and press for use in the foundry. I can remember the press and its cylinders - perhaps the records of the auctioneers could reveal their destinations.